Everyone tends to have a different idea on shipping plants. What I have found to work is pretty simple. Cut the stem and only allow the the water that drips off the plant to remain. More, the plant may turn to mush. I never wrap my plants in anything, some wrap in newspaper or paper towel. Often, it turns to mush but even when it does not, it's not uncommon for the plant to stick to it a bit and pull the leaves off or break the stem, which may mean the plant will take longer to recover. I personally use a larger box than needed and blow some air into the bag. It costs more but I usually don't have a small enough box anyway so it kind of works itself out, I pay a dollar or so more for shipping, save the money on the box.
Don't get me wrong, I have had the receiving party freak out that I didn't wrap the plants, just because it is so common to do so. The plants are not damaged but they are so used to it, they think it's required.
On ROAK's, I tend to just put everything into one bag but I try to tie all the speices together. I used to use plant weights but they can be hard to find lately. I may use the little metal twist ties in the future. If I am selling (or buying), I like them to be separated out with the bag labeled so I know what is what. It can be hard to tell sometimes after a few days of shipping, especially when buying an unfamiliar plant. I think one should go the extra mile when they are making money, as long as the shipping price is reasonable. You can also put dissimilar looking plants in the same bag, reducing the number of bags.
The only reason I put in the part of separating out the plants is it can be a huge pain to get a bag of plants that you have to separate out, then figure out exactly what is what. Simply labeling them and making things obvious only takes 5 more minutes at most on the seller's end but saves the buyer an hour, maybe hours, up to days to figure out exactly what things are.
Probably should go without saying but with any online business, you shouldn't cash out your PayPal until you know the item has been received and the buyer is happy. I know plenty of people who sold expensive things online, cashed out the payment before even sending the item, only to have some issue, then can't easily afford to pay up when a claim is made. That's only if you are selling, obviously, and more of a general statement but it's good practice.